Analyzers detecting the amounts of analytes in certain body fluids use a light source to illuminate test samples, which sources can vary (drift) in intensity over time. Usually conventional solutions require a machine reference determination, or alternatively, simultaneous readings of the light source used to illuminate the test samples, herein identified as "dual channel". In many applications, the dual channel approach is not preferred, because of cost. Hence, a machine reference reading is usually used.
In making these machine reference readings, a conventional procedure has been to read the reference value, store it, thereafter read the test sample, and compare the two. The "comparison" conventionally involves, for example, the use of the formula (sample--reference.sub.black)/ (reference.sub.white --reference.sub.black) as is listed in U.S. Pat. No. 4,566,798, column 1, line 40, where both a black and a white reference are used. Occasionally the reference element is read again to update that value, but the updated reading is only used for subsequent sample readings, and not previous sample readings. The problem is that the longer in time the reference reading is from the sample reading, the greater likelihood there is of drift in the light source.
We have discovered that this reference read procedure is not adequate. More specifically, the reference value tends to drift, and the drift is such that merely occasionally updating it does not adequately correct sample readings taken just prior to the update. Of course, a reference element could be positioned to be read every time and just prior to when a sample is to be read, but this is unsatisfactory as the number of reference readings would become too numerous. The end result would be increased cost for these reference elements and lack of through-put.
Yet another problem with many conventional analyzers is that, to make a reading of a sample at a new wavelength, say of 460 nm, it first needs to make a new reference element reading at that wavelength. Thus, every time a new wavelength is required for a new chemistry, a new reference element could be required for that new wavelength. Since only one wavelength can be used for a single scan of a reference element, if a new assay is added to an incubator with a single reference element, only previous or subsequent pass-throughs could generate a reading at the desired wavelength. As a result, there could be as many as 8 reference elements in an analyzer, for 8 different wavelengths used in the analysis. Such a multitude of wavelengths is not only expensive but occupies space that could otherwise be used for other purposes.